Now here we're going to say that peptides are formed when 2 or more amino acids bond with each other through a peptide bond. Now here we're going to say the peptide bond, also known as an amide bond, is when we have the carboxyl group of 1 amino acid covalently bonds with the amino group of another amino acid. Now pay attention here. We have the carboxyl group here in its anionic form, so its negatively charged forme, and we have the amino group in its positive charge form. Now if we come down here, we're talking about the formation of a peptide bond. We've kind of seen this before when we talked about the formation of an amide bond. Remember, that happens through a condensation reaction. We have the loss of water. So here we have alanine, which is our amino acid, and we have threonine here. We're going to say we're going to have the loss of water. So if we look at this, the loss of water, we would lose this oxygen here, and we'd lose 2 hydrogens here from the NH3 group. Right. So we have the loss of water here. Here we show this arrow. This arrow that's pointing up shows that we have the loss of water, so it's leaving the two structures. What's left behind combine together give us our peptide bond. So we lost this oxygen, we lost 2 hydrogens. Meaning that nitrogen still has 1 H on it. So that's why it's still here. We didn't touch anything in terms of this carbonyl group, so it's still intact. The bond they form is a result of them losing water. So now we have a dipeptide and we show this by giving the 3 letter code for each amino acid connected to each other by a hyphen. This hyphen here can represent this peptide bond between the two amino acids. Now here we're going to say that the number of amino acids and peptides is indicated by prefixes. So we know dí, tri, tetra. Here we're going to say that a polypeptide is a peptide consisting of a larger number of amino acid residues. And remember, a residue is just an individual amino acid contained within a peptide. Here, we call this a dipeptide, dí because it's 2 amino acids connected by 1 peptide bond. If we have 3 amino acids, then it would be a tripeptide. If we have 4 amino acids, it would be a tetra peptide. If we have beyond that, then we can start talking about it being a more complicated chain of amino acids connected by peptide bonds. Right. But just remember, we've seen something like this before when we talked about the formation of amide in earlier chapters. Now we're relating it to the connection of 2 different amino acids to one another. Right. So just remember, a peptide is 2 aminos connected by a peptide bond.
18. Amino Acids and Proteins
Peptides
Video duration:
3mRelated Videos
Related Practice
